1. Field of the Invention
The invention relates to an optical scanner assembly suited to an imaging systems for irradiating a plurality of image carriers such as photosensitive drums with a laser beam individually to form electrostatic latent images of identical or different colors on the respective image carriers, and successively transferring toner images formed from these electrostatic latent images while moving a transfer medium such as a sheet of recording paper, thereby forming a desired image on the transfer medium. In particular, the invention relates to an optical path structure extending from light sources to deflector means such as a polygon mirror.
2. Description of the Related Art
Tandem imaging systems are widely known as the color-imaging systems for use in the color copiers or the color printers. This imaging system employs a method of arranging a plurality of image carriers such as photosensitive drums in tandem, irradiating each of these image carriers with a laser beam under write scan to form electrostatic latent images, developing these electrostatic latent images with predetermined toners to form toner images, and successively transferring the toner images to a transfer medium such as a sheet of recording paper which is moved in the tandem direction of the image carriers to form a color image.
Among the typical imaging systems of this kind is an optical scanner system that appears in Japanese Patent Laid-Open Publication No. Hei 11-295625. Such a typical tandem imaging system is configured to form electrostatic latent images by exposing its four photosensitive drums to the laser beams emitted from four laser light sources corresponding to image data of Y (yellow), M (magenta), C (cyan), and BK (black) through corresponding optical scanner systems, respectively.
In this color imaging system, the plurality of photosensitive drums are provided with their respective optical scanner systems, which can hinder the miniaturization of the apparatus and result in higher cost. On this account, Japanese Patent Laid-Open Publications No. Hei 6-286226, 10-20608, 10-133131, and others have disclosed color imaging systems having a single optical scanner system common to a plurality of photosensitive drums to achieve the miniaturization of the system. The optical scanner assemblies used in these color imaging systems are configured so that a plurality of laser light sources consistent with the number of photosensitive bodies emit laser beams, deflector means for common deflection deflects the laser beams to splitter means, and the splitter means introduces the laser beams to the respective photosensitive bodies.
To form clearer latent images on the image carriers, the optical member introducing the laser beams to the image carriers must need to exhibit desired optical performance. In particular, the optical paths extending from the laser light source to the deflector means contain collimator lenses and cylindrical lenses, which carry out an adjustment to the laser beams. In order for these optical members to have the desired optical performance, appropriate lengths are required of the optical paths. For example, a laser beam passed through a cylindrical lens must be incident on the deflector means with proper convergence. This convergence necessitates an optical path of appropriate length.
For the sake of commonality of the optical members regarding the four laser beams emitted from the four laser light sources, the optical path lengths from the cylindrical lenses to the image carriers are desirably equal.
Also, conventional optical scanner assemblies have their cylindrical lenses spaced away from the polygon mirror. Thus, securing optical paths of appropriate lengths hinders the miniaturization of the optical scanner assemblies.
In view of the foregoing, an object of this invention is to provide an optical path structure for an optical scanner assembly which can secure desired optical path lengths and achieve the miniaturization of the optical scanner assembly as well.
As technical means to achieve the foregoing object, this invention provides an optical path structure of an optical scanner assembly for introducing three or more light beams to deflector means for deflection and passing the respective light beams deflected and reflected by the deflector means through an Fxcex8 lens to scan over image carriers individually, thereby forming electrostatic latent images on the image carriers, the optical path structure introducing the light beams from light sources to the image carriers. In plan view, a pair of Fxcex8 lenses are arranged at symmetrical positions about an axis of symmetry passing through the center of the deflector means. Three or more light sources for emitting the light beams are divided into two groups and arranged across the axis of symmetry. At least one of the light beams is incident on reflector means arranged on the other side of the axis of symmetry from the light source of the light beam. The rest of the light beams is/are incident on other reflector means arranged on the same side of the axis of symmetry as the light source(s) of the light beam(s). The light beams reflected from the reflector means are reflected by deflector reflective surfaces of the deflector means lying on the same sides of the axis of symmetry as the reflector means, and introduced to the Fxcex8 lenses, respectively.
The light source to emit the one light beam that is incident on the reflector means on the other side of the axis of symmetry is arranged close to a base line which passes through the center of the deflector means and crosses the axis of symmetry at right angles. The light sources of the other two light beams are arranged farther from the base line. That is, the one light beam is introduced to a deflector reflective surface of the deflector means on the farther side. The other two light beams are introduced to deflector reflective surfaces of the deflector means on the closer sides. Therefore, the optical path length of the one light beam and the optical path lengths of the two light beams can be easily adjusted to the same length.
In addition, the light source of the one light beam can be arranged with no wide space from the axis of symmetry. As a result, the optical path of that light beam up to the deflector means can be accommodated in a small region, which allows the miniaturization of the optical scanner assembly.
The optical path structure of an optical scanner assembly according to this invention is characterized in that the optical paths of light beams passed through the same Fxcex8 lens out of the pair of Fxcex8 lenses generally agree with each other where extending from the reflector means to the deflector reflective surface. Alternatively, the optical path structure of an optical scanner assembly according to the invention is characterized in that the optical path of a light beam reflected from the reflector means lying on the same side of the axis of symmetry as the light source thereof is arranged above that of a light beam reflected from the reflector means lying on the other side of the axis of symmetry from the light source thereof so that these optical paths generally agree with each other.
The general agreement of the optical paths facilitates the mounting and adjustment of such optical members as the reflector means. In addition, machining precision can be easily secured of the mounting portions of these optical members.
Another optical path structure of an optical scanner assembly according to this invention is an optical path structure of an optical scanner assembly for introducing three or more light beams to deflector means for deflection and passing the respective light beams deflected and reflected by the deflector means through an Fxcex8 lens to scan over image carriers individually, thereby forming electrostatic latent images on the image carriers, the optical path structure introducing the light beams from light sources to the image carriers. In plan view, a pair of Fxcex8 lenses are arranged at symmetrical positions about an axis of symmetry passing through the center of the deflector means. Three or more light sources for emitting the light beams are divided into two groups and arranged across the axis of symmetry. Reflector means for reflecting the respective light beams are arranged across the axis of symmetry. The light beam emitted from a light source on one side of the axis of symmetry is incident on the reflector means on the other side. The light beams reflected from the reflector means are reflected by deflector reflective surfaces of the deflector means lying on the same sides of the axis of symmetry as the reflector means, and introduced to the Fxcex8 lenses, respectively.
The light beams are all introduced so as to. be incident on the deflector reflective surfaces that lie on the other sides of the axis of symmetry from their respective light sources. That is, the light beams are incident on the deflector reflective surfaces farther from their light sources. Therefore, the optical path lengths up to the deflector reflective surfaces can be increased, whereby desired lengths can be secured easily. The optical paths can be accommodated in small regions. Besides, the optical path lengths of all the light beams can be easily made equal.
The optical path structure of an optical scanner assembly according to this invention is characterized in that optical paths extending from the light sources to the reflector means are generally orthogonal to the axis of symmetry. Alternatively, the optical path structure of an optical scanner assembly according to the invention is characterized in that optical paths extending from the light sources to the reflector means are not orthogonal to the axis of symmetry.
Whether to arrange the optical paths orthogonal or oblique to the axis of symmetry may be determined depending on such factors as the arrangement and structure of the individual parts of this optical scanner assembly. The oblique arrangement can secure greater optical path lengths than in the case of the orthogonal arrangement, thereby allowing easy adjustment for equal optical path lengths. In the orthogonal arrangement, on the other hand, the optical paths are oriented along the X- and Y-axes, or the bases for mounting and adjusting the individual parts of this optical scanner assembly. The clearer bases of measurement as to the optical paths facilitate the verification of the mounting precision and the like.
The optical path structure of an optical scanner assembly according to this invention is characterized in that the light sources and the reflector means are arranged at symmetrical positions about the axis of symmetry.
When the optical paths are oblique to the axis of symmetry, the optical paths can be prevented from overlapping. This allows symmetric arrangement of the light sources and the reflector means. Cylindrical lenses and the like which carry out an adjustment to the light beams can also be arranged symmetrically. When the optical members are arranged symmetrically, parts deformations resulting from the influence of temperature and the like equally act on the parts lying in symmetrical positions. This can make the optical members less susceptible to the influence.
Another optical path structure of an optical scanner assembly according to this invention is an optical path structure of an optical scanner assembly for introducing four light beams to deflector means for deflection and passing the respective light beams deflected and reflected by the deflector means through an Fxcex8 lens to scan over image carriers individually, thereby forming electrostatic latent images on the image carriers, the optical path structure introducing the light beams from light sources to the image carriers. In plan view, a pair of Fxcex8 lenses are arranged at symmetrical positions about an axis of symmetry passing through the center of the deflector means. Four light sources for emitting the light beams are divided into two pairs and arranged across the axis of symmetry. Reflector means for reflecting the respective light beams are arranged across the axis of symmetry. The light beam emitted from one of the light sources arranged on one side of the axis of symmetry and the light beam emitted from the other light source are incident on the reflector means on the other side and on the same side, respectively. The light beams reflected from the reflector means are reflected by deflector reflective surfaces of the deflector means lying on the same sides of the axis of symmetry as the reflector means, and introduced to the Fxcex8 lenses, respectively.
A color imaging system uses four laser beams for carrying image data of Y, M, C, and BK, respectively. Thus, four light sources are typically in use. The light beams emitted from the light sources arranged closer to the base line are incident on the reflector means that are arranged farther from the base line on the same sides of the axis of symmetry as the light sources are. Meanwhile, the light beams emitted from the light sources arranged farther from the base line are incident on the reflector means that are arranged closer to base line on the other sides of the axis of symmetry from the light sources are. On this account, the optical path lengths of the light beams can be made yet greater. The optical path lengths can be easily made equal.
The above and other objects, features and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments of the invention in conjunction with the accompanying drawings, in which: